In steering systems with an electric motor servo drive, acting via a ball screw drive, the ball nut is either mounted rotatably and axially rigidly in the housing or the ball nut allows a certain lengthwise and tilting movement thanks to the use of spring elements and special design of the housing or the bearing. A spherical bearing in which both the bearing ring and the frame have a spherical surface is likewise known. In this design, the midpoint of the ball surface is designed to lie in the center plane of the bearing. Similar functions are made possible by spherical roller bearings and self-aligning roller bearings, which tolerate an angular error of the shaft. The goal of these bearings is to even out the tolerance, thereby preventing stresses in the ball screw drive. Moreover, the dynamic and static loading of the structural parts is reduced. The result is improved acoustical properties and reduction in mechanical looseness caused by thermal expansion of the components.
In the described bearing, the problem occurs between the spherical surfaces, just as when using spherical roller bearings and self-aligning roller bearings, that these bearings are more designed for radial forces. But the loads occurring on the ball nut in an electrically assisted steering drive are primarily axially oriented in regard to the steering rack or threaded spindle.
DE 103 10 492 A1 describes a power steering system, especially for motor vehicles, with a servomotor formed as an electric motor, which drives an axially movable component configured as a push rod via a nut which is able to rotate in a frame formed as a steering housing, but unable to move axially. The servomotor, the push rod and the nut are mounted by means of an eccentric bearing ring such that the axial distance between the motor shaft of the servomotor and the push rod is variable, which allows for a quick and easy installation of the power steering system.
An electrical steering device is known from DE 102 02 483 A1, having a toothed rack connected to a steering spindle, a motor to assist a steering force with a rotor arranged coaxially on the toothed rack, a spindle drive in which balls are inserted between a nut keyed to the rotor and a screw formed on the toothed rack, and having a housing which is approximately cylindrical as a whole. The nut of the ball screw mechanism is mounted rotatably in a bearing inside the nut housing section.
DE 1947337 U presents an elastic roller bearing, which has an axial mobility and an axial spring action with restoring force. A roller bearing with an outer race and an inner race, the outer race and/or the inner race each being arranged between at least one dampening element, is known from DE 10 2004 034 701 A1.
EP 1 571 067 A1 discloses the elastic bearing of a worm shaft which coaxially encircles the motor shaft of a servomotor.
The relevant prior art EP 2 049 383 81 shows a solution for enabling or improving the swiveling of a radial bearing. A convex bulge is provided on the outer circumference of the outer race, or the nut on which the inner race sits is provided with a convex bulge. Thanks to the convex bulge of the outer circumference of the outer race or that of the nut, a releasing of the radial bearing and a swiveling of the nut and the axially movable component is achieved. At each end face of the radial bearing there is provided a steel ring on which is vulcanized an element with elastomer properties, making possible an axial and radial dampening as well as a pass through and dampening of the swiveling movement of the axially movable component under alternating loads. When the axially movable component is subjected to bending torque, a seizing of the system should be prevented. The fabrication of the elements used and the installation of the elements are time-consuming. Furthermore, a desirable dampening of the bearing with low installation height is not disclosed in the prior art.
A plate spring arrangement is known from DE 10 2009 019 856 A1 in which at least two coated plate springs form a plate stack, and an elastic intermediate layer is arranged between the coated plate springs, enabling a relative movement of the two plate springs separated by the intermediate layer thanks to shear action. The parallel coupling of the springs can accomplish a force boosting, the springs being preferably elastically coupled and free of friction.